
package ch.ethz.ssh2;

import java.io.CharArrayWriter;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.net.SocketTimeoutException;
import java.security.SecureRandom;
import java.util.Vector;

import ch.ethz.ssh2.auth.AuthenticationManager;
import ch.ethz.ssh2.channel.ChannelManager;
import ch.ethz.ssh2.crypto.CryptoWishList;
import ch.ethz.ssh2.crypto.cipher.BlockCipherFactory;
import ch.ethz.ssh2.crypto.digest.MAC;
import ch.ethz.ssh2.transport.KexManager;
import ch.ethz.ssh2.transport.TransportManager;
import ch.ethz.ssh2.util.TimeoutService;
import ch.ethz.ssh2.util.TimeoutService.TimeoutToken;

/**
 * A <code>Connection</code> is used to establish an encrypted TCP/IP
 * connection to a SSH-2 server.
 * <p>
 * Typically, one
 * <ol>
 * <li>creates a {@link #Connection(String) Connection} object.</li>
 * <li>calls the {@link #connect() connect()} method.</li>
 * <li>calls some of the authentication methods (e.g., {@link #authenticateWithPublicKey(String, File, String) authenticateWithPublicKey()}).</li>
 * <li>calls one or several times the {@link #openSession() openSession()} method.</li>
 * <li>finally, one must close the connection and release resources with the {@link #close() close()} method.</li>
 * </ol>
 * 
 * @author Christian Plattner, plattner@inf.ethz.ch
 * @version $Id: Connection.java,v 1.28 2006/09/12 15:35:26 cplattne Exp $
 */

public class Connection
{
	/**
	 * The identifier presented to the SSH-2 server.
	 */
	public final static String identification = "Ganymed Build_210";

	/* Will be used to generate all random data needed for the current connection.
	 * Note: SecureRandom.nextBytes() is thread safe.
	 */

	private SecureRandom generator;

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @return The list of supported cipher algorithms by this implementation.
	 */
	public static synchronized String[] getAvailableCiphers()
	{
		return BlockCipherFactory.getDefaultCipherList();
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @return The list of supported MAC algorthims by this implementation.
	 */
	public static synchronized String[] getAvailableMACs()
	{
		return MAC.getMacList();
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @return The list of supported server host key algorthims by this implementation.
	 */
	public static synchronized String[] getAvailableServerHostKeyAlgorithms()
	{
		return KexManager.getDefaultServerHostkeyAlgorithmList();
	}

	private AuthenticationManager am;

	private boolean authenticated = false;
	private ChannelManager cm;

	private CryptoWishList cryptoWishList = new CryptoWishList();

	private DHGexParameters dhgexpara = new DHGexParameters();

	private final String hostname;

	private final int port;

	private TransportManager tm;

	private boolean tcpNoDelay = false;

	private ProxyData proxyData = null;

	private Vector connectionMonitors = new Vector();

	/**
	 * Prepares a fresh <code>Connection</code> object which can then be used
	 * to establish a connection to the specified SSH-2 server.
	 * <p>
	 * Same as {@link #Connection(String, int) Connection(hostname, 22)}. 
	 * 
	 * @param hostname the hostname of the SSH-2 server.
	 */
	public Connection(String hostname)
	{
		this(hostname, 22);
	}

	/**
	 * Prepares a fresh <code>Connection</code> object which can then be used
	 * to establish a connection to the specified SSH-2 server.
	 * 
	 * @param hostname
	 *            the host where we later want to connect to.
	 * @param port
	 *            port on the server, normally 22.
	 */
	public Connection(String hostname, int port)
	{
		this.hostname = hostname;
		this.port = port;
	}

	/**
	 * After a successful connect, one has to authenticate oneself. This method
	 * is based on DSA (it uses DSA to sign a challenge sent by the server).
	 * <p>
	 * If the authentication phase is complete, <code>true</code> will be
	 * returned. If the server does not accept the request (or if further
	 * authentication steps are needed), <code>false</code> is returned and
	 * one can retry either by using this or any other authentication method
	 * (use the <code>getRemainingAuthMethods</code> method to get a list of
	 * the remaining possible methods).
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param pem
	 *            A <code>String</code> containing the DSA private key of the
	 *            user in OpenSSH key format (PEM, you can't miss the
	 *            "-----BEGIN DSA PRIVATE KEY-----" tag). The string may contain
	 *            linefeeds.
	 * @param password
	 *            If the PEM string is 3DES encrypted ("DES-EDE3-CBC"), then you
	 *            must specify the password. Otherwise, this argument will be
	 *            ignored and can be set to <code>null</code>.
	 * 
	 * @return whether the connection is now authenticated.
	 * @throws IOException
	 * 
	 * @deprecated You should use one of the {@link #authenticateWithPublicKey(String, File, String) authenticateWithPublicKey()}
	 * 		      methods, this method is just a wrapper for it and will
	 *            disappear in future builds.
	 * 
	 */
	public synchronized boolean authenticateWithDSA(String user, String pem, String password) throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Connection is not established!");

		if (authenticated)
			throw new IllegalStateException("Connection is already authenticated!");

		if (am == null)
			am = new AuthenticationManager(tm);

		if (cm == null)
			cm = new ChannelManager(tm);

		if (user == null)
			throw new IllegalArgumentException("user argument is null");

		if (pem == null)
			throw new IllegalArgumentException("pem argument is null");

		authenticated = am.authenticatePublicKey(user, pem.toCharArray(), password, getOrCreateSecureRND());

		return authenticated;
	}

	/**
	 * A wrapper that calls {@link #authenticateWithKeyboardInteractive(String, String[], InteractiveCallback)
	 * authenticateWithKeyboardInteractivewith} a <code>null</code> submethod list.
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param cb
	 *            An <code>InteractiveCallback</code> which will be used to
	 *            determine the responses to the questions asked by the server.
	 * @return whether the connection is now authenticated.
	 * @throws IOException
	 */
	public synchronized boolean authenticateWithKeyboardInteractive(String user, InteractiveCallback cb)
			throws IOException
	{
		return authenticateWithKeyboardInteractive(user, null, cb);
	}

	/**
	 * After a successful connect, one has to authenticate oneself. This method
	 * is based on "keyboard-interactive", specified in
	 * draft-ietf-secsh-auth-kbdinteract-XX. Basically, you have to define a
	 * callback object which will be feeded with challenges generated by the
	 * server. Answers are then sent back to the server. It is possible that the
	 * callback will be called several times during the invocation of this
	 * method (e.g., if the server replies to the callback's answer(s) with
	 * another challenge...)
	 * <p>
	 * If the authentication phase is complete, <code>true</code> will be
	 * returned. If the server does not accept the request (or if further
	 * authentication steps are needed), <code>false</code> is returned and
	 * one can retry either by using this or any other authentication method
	 * (use the <code>getRemainingAuthMethods</code> method to get a list of
	 * the remaining possible methods).
	 * <p>
	 * Note: some SSH servers advertise "keyboard-interactive", however, any
	 * interactive request will be denied (without having sent any challenge to
	 * the client).
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param submethods
	 *            An array of submethod names, see
	 *            draft-ietf-secsh-auth-kbdinteract-XX. May be <code>null</code>
	 *            to indicate an empty list.
	 * @param cb
	 *            An <code>InteractiveCallback</code> which will be used to
	 *            determine the responses to the questions asked by the server.
	 * 
	 * @return whether the connection is now authenticated.
	 * @throws IOException
	 */
	public synchronized boolean authenticateWithKeyboardInteractive(String user, String[] submethods,
			InteractiveCallback cb) throws IOException
	{
		if (cb == null)
			throw new IllegalArgumentException("Callback may not ne NULL!");

		if (tm == null)
			throw new IllegalStateException("Connection is not established!");

		if (authenticated)
			throw new IllegalStateException("Connection is already authenticated!");

		if (am == null)
			am = new AuthenticationManager(tm);

		if (cm == null)
			cm = new ChannelManager(tm);

		if (user == null)
			throw new IllegalArgumentException("user argument is null");

		authenticated = am.authenticateInteractive(user, submethods, cb);

		return authenticated;
	}

	/**
	 * After a successfull connect, one has to authenticate oneself. This method
	 * sends username and password to the server.
	 * <p>
	 * If the authentication phase is complete, <code>true</code> will be
	 * returned. If the server does not accept the request (or if further
	 * authentication steps are needed), <code>false</code> is returned and
	 * one can retry either by using this or any other authentication method
	 * (use the <code>getRemainingAuthMethods</code> method to get a list of
	 * the remaining possible methods).
	 * <p>
	 * Note: if this method fails, then please double-check that it is actually
	 * offered by the server (use {@link #getRemainingAuthMethods(String) getRemainingAuthMethods()}.
	 * <p>
	 * Often, password authentication is disabled, but users are not aware of it.
	 * Many servers only offer "publickey" and "keyboard-interactive". However,
	 * even though "keyboard-interactive" *feels* like password authentication
	 * (e.g., when using the putty or openssh clients) it is *not* the same mechanism.
	 * 
	 * @param user
	 * @param password
	 * @return if the connection is now authenticated.
	 * @throws IOException
	 */
	public synchronized boolean authenticateWithPassword(String user, String password) throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Connection is not established!");

		if (authenticated)
			throw new IllegalStateException("Connection is already authenticated!");

		if (am == null)
			am = new AuthenticationManager(tm);

		if (cm == null)
			cm = new ChannelManager(tm);

		if (user == null)
			throw new IllegalArgumentException("user argument is null");

		if (password == null)
			throw new IllegalArgumentException("password argument is null");

		authenticated = am.authenticatePassword(user, password);

		return authenticated;
	}

	/**
	 * After a successful connect, one has to authenticate oneself.
	 * The authentication method "publickey" works by signing a challenge
	 * sent by the server. The signature is either DSA or RSA based - it
	 * just depends on the type of private key you specify, either a DSA
	 * or RSA private key in PEM format. And yes, this is may seem to be a
	 * little confusing, the method is called "publickey" in the SSH-2 protocol
	 * specification, however since we need to generate a signature, you
	 * actually have to supply a private key =).
	 * <p>
	 * The private key contained in the PEM file may also be encrypted ("Proc-Type: 4,ENCRYPTED").
	 * The library supports DES-CBC and DES-EDE3-CBC encryption, as well
	 * as the more exotic PEM encrpytions AES-128-CBC, AES-192-CBC and AES-256-CBC.
	 * <p>
	 * If the authentication phase is complete, <code>true</code> will be
	 * returned. If the server does not accept the request (or if further
	 * authentication steps are needed), <code>false</code> is returned and
	 * one can retry either by using this or any other authentication method
	 * (use the <code>getRemainingAuthMethods</code> method to get a list of
	 * the remaining possible methods).
	 * <p>
	 * NOTE PUTTY USERS: Event though your key file may start with "-----BEGIN..."
	 * it is not in the expected format. You have to convert it to the OpenSSH
	 * key format by using the "puttygen" tool (can be downloaded from the Putty
	 * website). Simply load your key and then use the "Conversions/Export OpenSSH key"
	 * functionality to get a proper PEM file.
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param pemPrivateKey
	 *            A <code>char[]</code> containing a DSA or RSA private key of the
	 *            user in OpenSSH key format (PEM, you can't miss the
	 *            "-----BEGIN DSA PRIVATE KEY-----" or "-----BEGIN RSA PRIVATE KEY-----"
	 *            tag). The char array may contain linebreaks/linefeeds.
	 * @param password
	 *            If the PEM structure is encrypted ("Proc-Type: 4,ENCRYPTED") then
	 *            you must specify a password. Otherwise, this argument will be ignored
	 *            and can be set to <code>null</code>.
	 * 
	 * @return whether the connection is now authenticated.
	 * @throws IOException
	 */
	public synchronized boolean authenticateWithPublicKey(String user, char[] pemPrivateKey, String password)
			throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Connection is not established!");

		if (authenticated)
			throw new IllegalStateException("Connection is already authenticated!");

		if (am == null)
			am = new AuthenticationManager(tm);

		if (cm == null)
			cm = new ChannelManager(tm);

		if (user == null)
			throw new IllegalArgumentException("user argument is null");

		if (pemPrivateKey == null)
			throw new IllegalArgumentException("pemPrivateKey argument is null");

		authenticated = am.authenticatePublicKey(user, pemPrivateKey, password, getOrCreateSecureRND());

		return authenticated;
	}

	/**
	 * A convenience wrapper function which reads in a private key (PEM format, either DSA or RSA)
	 * and then calls <code>authenticateWithPublicKey(String, char[], String)</code>.
	 * <p>
	 * NOTE PUTTY USERS: Event though your key file may start with "-----BEGIN..."
	 * it is not in the expected format. You have to convert it to the OpenSSH
	 * key format by using the "puttygen" tool (can be downloaded from the Putty
	 * website). Simply load your key and then use the "Conversions/Export OpenSSH key"
	 * functionality to get a proper PEM file.
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param pemFile
	 *            A <code>File</code> object pointing to a file containing a DSA or RSA
	 *            private key of the user in OpenSSH key format (PEM, you can't miss the
	 *            "-----BEGIN DSA PRIVATE KEY-----" or "-----BEGIN RSA PRIVATE KEY-----"
	 *            tag).
	 * @param password
	 *            If the PEM file is encrypted then you must specify the password.
	 *            Otherwise, this argument will be ignored and can be set to <code>null</code>.
	 * 
	 * @return whether the connection is now authenticated.
	 * @throws IOException
	 */
	public synchronized boolean authenticateWithPublicKey(String user, File pemFile, String password)
			throws IOException
	{
		if (pemFile == null)
			throw new IllegalArgumentException("pemFile argument is null");

		char[] buff = new char[256];

		CharArrayWriter cw = new CharArrayWriter();

		FileReader fr = new FileReader(pemFile);

		while (true)
		{
			int len = fr.read(buff);
			if (len < 0)
				break;
			cw.write(buff, 0, len);
		}

		fr.close();

		return authenticateWithPublicKey(user, cw.toCharArray(), password);
	}

	/**
	 * Add a {@link ConnectionMonitor} to this connection. Can be invoked at any time,
	 * but it is best to add connection monitors before invoking
	 * <code>connect()</code> to avoid glitches (e.g., you add a connection monitor after
	 * a successful connect(), but the connection has died in the mean time. Then,
	 * your connection monitor won't be notified.) 
	 * <p>
	 * You can add as many monitors as you like.
	 * 
	 * @see ConnectionMonitor
	 * 
	 * @param cmon An object implementing the <code>ConnectionMonitor</code> interface.
	 */
	public synchronized void addConnectionMonitor(ConnectionMonitor cmon)
	{
		if (cmon == null)
			throw new IllegalArgumentException("cmon argument is null");

		connectionMonitors.addElement(cmon);

		if (tm != null)
			tm.setConnectionMonitors(connectionMonitors);
	}

	/**
	 * Close the connection to the SSH-2 server. All assigned sessions will be
	 * closed, too. Can be called at any time. Don't forget to call this once
	 * you don't need a connection anymore - otherwise the receiver thread may
	 * run forever.
	 */
	public synchronized void close()
	{
		Throwable t = new Throwable("Closed due to user request.");
		close(t, false);
	}

	private void close(Throwable t, boolean hard)
	{
		if (cm != null)
			cm.closeAllChannels();

		if (tm != null)
		{
			tm.close(t, hard == false);
			tm = null;
		}
		am = null;
		cm = null;
		authenticated = false;
	}

	/**
	 * Same as {@link #connect(ServerHostKeyVerifier, int, int) connect(null, 0, 0)}.
	 * 
	 * @return see comments for the {@link #connect(ServerHostKeyVerifier, int, int) connect(ServerHostKeyVerifier, int, int)} method.
	 * @throws IOException
	 */
	public synchronized ConnectionInfo connect() throws IOException
	{
		return connect(null, 0, 0);
	}

	/**
	 * Same as {@link #connect(ServerHostKeyVerifier, int, int) connect(verifier, 0, 0)}.
	 * 
	 * @return see comments for the {@link #connect(ServerHostKeyVerifier, int, int) connect(ServerHostKeyVerifier, int, int)} method.
	 * @throws IOException
	 */
	public synchronized ConnectionInfo connect(ServerHostKeyVerifier verifier) throws IOException
	{
		return connect(verifier, 0, 0);
	}

	/**
	 * Connect to the SSH-2 server and, as soon as the server has presented its
	 * host key, use the {@link ServerHostKeyVerifier#verifyServerHostKey(String,
	 * int, String, byte[]) ServerHostKeyVerifier.verifyServerHostKey()}
	 * method of the <code>verifier</code> to ask for permission to proceed.
	 * If <code>verifier</code> is <code>null</code>, then any host key will be
	 * accepted - this is NOT recommended, since it makes man-in-the-middle attackes
	 * VERY easy (somebody could put a proxy SSH server between you and the real server).
	 * <p>
	 * Note: The verifier will be called before doing any crypto calculations
	 * (i.e., diffie-hellman). Therefore, if you don't like the presented host key then
	 * no CPU cycles are wasted (and the evil server has less information about us).
	 * <p>
	 * However, it is still possible that the server presented a fake host key: the server
	 * cheated (typically a sign for a man-in-the-middle attack) and is not able to generate
	 * a signature that matches its host key. Don't worry, the library will detect such
	 * a scenario later when checking the signature (the signature cannot be checked before
	 * having completed the diffie-hellman exchange).
	 * <p>
	 * Note 2: The  {@link ServerHostKeyVerifier#verifyServerHostKey(String,
	 * int, String, byte[]) ServerHostKeyVerifier.verifyServerHostKey()} method
	 * will *NOT* be called from the current thread, the call is being made from a
	 * background thread (there is a background dispatcher thread for every
	 * established connection). 
	 * <p>
	 * Note 3: This method will block as long as the key exchange of the underlying connection
	 * has not been completed (and you have not specified any timeouts).
	 * <p>
	 * Note 4: If you want to re-use a connection object that was successfully connected,
	 * then you must call the {@link #close()} method before invoking <code>connect()</code> again.
	 * 
	 * @param verifier
	 *            An object that implements the
	 *            {@link ServerHostKeyVerifier} interface. Pass <code>null</code>
	 *            to accept any server host key - NOT recommended.
	 *            
	 * @param connectTimeout
	 *            Connect the underlying TCP socket to the server with the given timeout
	 *            value (non-negative, in milliseconds). Zero means no timeout. If a proxy is being
	 *            used (see {@link #setProxyData(ProxyData)}), then this timeout is used for the
	 *            connection establishment to the proxy.
	 * 
	 * @param kexTimeout
	 *            Timeout for complete connection establishment (non-negative,
	 *            in milliseconds). Zero means no timeout. The timeout counts from the
	 *            moment you invoke the connect() method and is cancelled as soon as the
	 *            first key-exchange round has finished. It is possible that
	 *            the timeout event will be fired during the invocation of the
	 *            <code>verifier</code> callback, but it will only have an effect after
	 *            the <code>verifier</code> returns.
	 *            
	 * @return A {@link ConnectionInfo} object containing the details of
	 *            the established connection.
	 *         
	 * @throws IOException
	 *            If any problem occurs, e.g., the server's host key is not
	 *            accepted by the <code>verifier</code> or there is problem during
	 *            the initial crypto setup (e.g., the signature sent by the server is wrong).
	 *            <p>
	 *            In case of a timeout (either connectTimeout or kexTimeout)
	 *            a SocketTimeoutException is thrown.
	 *            <p>
	 *            An exception may also be thrown if the connection was already successfully
	 *            connected (no matter if the connection broke in the mean time) and you invoke
	 *            <code>connect()</code> again without having called {@link #close()} first.
	 *            <p>
	 *            If a HTTP proxy is being used and the proxy refuses the connection,
	 *            then a {@link HTTPProxyException} may be thrown, which
	 *            contains the details returned by the proxy. If the proxy is buggy and does
	 *            not return a proper HTTP response, then a normal IOException is thrown instead.        
	 */
	public synchronized ConnectionInfo connect(ServerHostKeyVerifier verifier, int connectTimeout, int kexTimeout)
			throws IOException
	{
		final class TimeoutState
		{
			boolean isCancelled = false;
			boolean timeoutSocketClosed = false;
		}

		if (tm != null)
			throw new IOException("Connection to " + hostname + " is already in connected state!");

		if (connectTimeout < 0)
			throw new IllegalArgumentException("connectTimeout must be non-negative!");

		if (kexTimeout < 0)
			throw new IllegalArgumentException("kexTimeout must be non-negative!");

		final TimeoutState state = new TimeoutState();

		tm = new TransportManager(hostname, port);

		tm.setConnectionMonitors(connectionMonitors);

		/* Make sure that the runnable below will observe the new value of "tm"
		 * and "state" (the runnable will be executed in a different thread, which
		 * may be already running, that is why we need a memory barrier here).
		 * See also the comment in Channel.java if you
		 * are interested in the details.
		 * 
		 * OKOK, this is paranoid since adding the runnable to the todo list
		 * of the TimeoutService will ensure that all writes have been flushed
		 * before the Runnable reads anything
		 * (there is a synchronized block in TimeoutService.addTimeoutHandler).
		 */

		synchronized (tm)
		{
			/* We could actually synchronize on anything. */
		}

		try
		{
			TimeoutToken token = null;

			if (kexTimeout > 0)
			{
				final Runnable timeoutHandler = new Runnable()
				{
					public void run()
					{
						synchronized (state)
						{
							if (state.isCancelled)
								return;
							state.timeoutSocketClosed = true;
							tm.close(new SocketTimeoutException("The connect timeout expired"), false);
						}
					}
				};

				long timeoutHorizont = System.currentTimeMillis() + kexTimeout;

				token = TimeoutService.addTimeoutHandler(timeoutHorizont, timeoutHandler);
			}

			try
			{
				tm.initialize(cryptoWishList, verifier, dhgexpara, connectTimeout, getOrCreateSecureRND(), proxyData);
			}
			catch (SocketTimeoutException se)
			{
				throw (SocketTimeoutException) new SocketTimeoutException(
						"The connect() operation on the socket timed out.").initCause(se);
			}

			tm.setTcpNoDelay(tcpNoDelay);

			/* Wait until first KEX has finished */

			ConnectionInfo ci = tm.getConnectionInfo(1);

			/* Now try to cancel the timeout, if needed */

			if (token != null)
			{
				TimeoutService.cancelTimeoutHandler(token);

				/* Were we too late? */

				synchronized (state)
				{
					if (state.timeoutSocketClosed)
						throw new IOException("This exception will be replaced by the one below =)");
					/* Just in case the "cancelTimeoutHandler" invocation came just a little bit
					 * too late but the handler did not enter the semaphore yet - we can
					 * still stop it.
					 */
					state.isCancelled = true;
				}
			}

			return ci;
		}
		catch (SocketTimeoutException ste)
		{
			throw ste;
		}
		catch (IOException e1)
		{
			/* This will also invoke any registered connection monitors */
			close(new Throwable("There was a problem during connect."), false);

			synchronized (state)
			{
				/* Show a clean exception, not something like "the socket is closed!?!" */
				if (state.timeoutSocketClosed)
					throw new SocketTimeoutException("The kexTimeout (" + kexTimeout + " ms) expired.");
			}

			/* Do not wrap a HTTPProxyException */
			if (e1 instanceof HTTPProxyException)
				throw e1;

			throw (IOException) new IOException("There was a problem while connecting to " + hostname + ":" + port)
					.initCause(e1);
		}
	}

	/**
	 * Creates a new {@link LocalPortForwarder}.
	 * A <code>LocalPortForwarder</code> forwards TCP/IP connections that arrive at a local
	 * port via the secure tunnel to another host (which may or may not be
	 * identical to the remote SSH-2 server).
	 * <p>
	 * This method must only be called after one has passed successfully the authentication step.
	 * There is no limit on the number of concurrent forwardings.
	 * 
	 * @param local_port the local port the LocalPortForwarder shall bind to.
	 * @param host_to_connect target address (IP or hostname)
	 * @param port_to_connect target port
	 * @return A {@link LocalPortForwarder} object.
	 * @throws IOException
	 */
	public synchronized LocalPortForwarder createLocalPortForwarder(int local_port, String host_to_connect,
			int port_to_connect) throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Cannot forward ports, you need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("Cannot forward ports, connection is not authenticated.");

		return new LocalPortForwarder(cm, local_port, host_to_connect, port_to_connect);
	}

	/**
	 * Creates a new {@link LocalStreamForwarder}.
	 * A <code>LocalStreamForwarder</code> manages an Input/Outputstream pair
	 * that is being forwarded via the secure tunnel into a TCP/IP connection to another host
	 * (which may or may not be identical to the remote SSH-2 server).
	 * 
	 * @param host_to_connect
	 * @param port_to_connect
	 * @return A {@link LocalStreamForwarder} object.
	 * @throws IOException
	 */
	public synchronized LocalStreamForwarder createLocalStreamForwarder(String host_to_connect, int port_to_connect)
			throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Cannot forward, you need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("Cannot forward, connection is not authenticated.");

		return new LocalStreamForwarder(cm, host_to_connect, port_to_connect);
	}

	/**
	 * Create a very basic {@link SCPClient} that can be used to copy
	 * files from/to the SSH-2 server.
	 * <p>
	 * Works only after one has passed successfully the authentication step.
	 * There is no limit on the number of concurrent SCP clients.
	 * <p>
	 * Note: This factory method will probably disappear in the future.
	 * 
	 * @return A {@link SCPClient} object.
	 * @throws IOException
	 */
	public synchronized SCPClient createSCPClient() throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Cannot create SCP client, you need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("Cannot create SCP client, connection is not authenticated.");

		return new SCPClient(this);
	}

	/**
	 * Force an asynchronous key re-exchange (the call does not block). The
	 * latest values set for MAC, Cipher and DH group exchange parameters will
	 * be used. If a key exchange is currently in progress, then this method has
	 * the only effect that the so far specified parameters will be used for the
	 * next (server driven) key exchange.
	 * <p>
	 * Note: This implementation will never start a key exchange (other than the initial one)
	 * unless you or the SSH-2 server ask for it.
	 * 
	 * @throws IOException
	 *             In case of any failure behind the scenes.
	 */
	public synchronized void forceKeyExchange() throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("You need to establish a connection first.");

		tm.forceKeyExchange(cryptoWishList, dhgexpara);
	}

	/**
	 * Returns the hostname that was passed to the constructor.
	 * 
	 * @return the hostname
	 */
	public synchronized String getHostname()
	{
		return hostname;
	}

	/**
	 * Returns the port that was passed to the constructor.
	 * 
	 * @return the TCP port
	 */
	public synchronized int getPort()
	{
		return port;
	}

	/**
	 * Returns a {@link ConnectionInfo} object containing the details of
	 * the connection. Can be called as soon as the connection has been
	 * established (successfully connected).
	 * 
	 * @return A {@link ConnectionInfo} object.
	 * @throws IOException
	 *             In case of any failure behind the scenes.
	 */
	public synchronized ConnectionInfo getConnectionInfo() throws IOException
	{
		if (tm == null)
			throw new IllegalStateException(
					"Cannot get details of connection, you need to establish a connection first.");
		return tm.getConnectionInfo(1);
	}

	/**
	 * After a successful connect, one has to authenticate oneself. This method
	 * can be used to tell which authentication methods are supported by the
	 * server at a certain stage of the authentication process (for the given
	 * username).
	 * <p>
	 * Note 1: the username will only be used if no authentication step was done
	 * so far (it will be used to ask the server for a list of possible
	 * authentication methods). Otherwise, this method ignores the user name and
	 * returns a cached method list (which is based on the information contained
	 * in the last negative server response).
	 * <p>
	 * Note 2: the server may return method names that are not supported by this
	 * implementation.
	 * <p>
	 * After a successful authentication, this method must not be called
	 * anymore.
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * 
	 * @return a (possibly emtpy) array holding authentication method names.
	 * @throws IOException
	 */
	public synchronized String[] getRemainingAuthMethods(String user) throws IOException
	{
		if (user == null)
			throw new IllegalArgumentException("user argument may not be NULL!");

		if (tm == null)
			throw new IllegalStateException("Connection is not established!");

		if (authenticated)
			throw new IllegalStateException("Connection is already authenticated!");

		if (am == null)
			am = new AuthenticationManager(tm);

		if (cm == null)
			cm = new ChannelManager(tm);

		return am.getRemainingMethods(user);
	}

	/**
	 * Determines if the authentication phase is complete. Can be called at any
	 * time.
	 * 
	 * @return <code>true</code> if no further authentication steps are
	 *         needed.
	 */
	public synchronized boolean isAuthenticationComplete()
	{
		return authenticated;
	}

	/**
	 * Returns true if there was at least one failed authentication request and
	 * the last failed authentication request was marked with "partial success"
	 * by the server. This is only needed in the rare case of SSH-2 server setups
	 * that cannot be satisfied with a single successful authentication request
	 * (i.e., multiple authentication steps are needed.)
	 * <p>
	 * If you are interested in the details, then have a look at
	 * draft-ietf-secsh-userauth-XX.txt.
	 * 
	 * @return if the there was a failed authentication step and the last one
	 *         was marked as a "partial success".
	 */
	public synchronized boolean isAuthenticationPartialSuccess()
	{
		if (am == null)
			return false;

		return am.getPartialSuccess();
	}

	/**
	 * Checks if a specified authentication method is available. This method is
	 * actually just a wrapper for {@link #getRemainingAuthMethods(String)
	 * getRemainingAuthMethods()}.
	 * 
	 * @param user
	 *            A <code>String</code> holding the username.
	 * @param method
	 *            An authentication method name (e.g., "publickey", "password",
	 *            "keyboard-interactive") as specified by the SSH-2 standard.
	 * @return if the specified authentication method is currently available.
	 * @throws IOException
	 */
	public synchronized boolean isAuthMethodAvailable(String user, String method) throws IOException
	{
		if (method == null)
			throw new IllegalArgumentException("method argument may not be NULL!");

		String methods[] = getRemainingAuthMethods(user);

		for (int i = 0; i < methods.length; i++)
		{
			if (methods[i].compareTo(method) == 0)
				return true;
		}

		return false;
	}

	private final SecureRandom getOrCreateSecureRND()
	{
		if (generator == null)
			generator = new SecureRandom();
		
		return generator;
	}
	
	/**
	 * Open a new {@link Session} on this connection. Works only after one has passed
	 * successfully the authentication step. There is no limit on the number of
	 * concurrent sessions.
	 * 
	 * @return A {@link Session} object.
	 * @throws IOException
	 */
	public synchronized Session openSession() throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("Cannot open session, you need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("Cannot open session, connection is not authenticated.");

		return new Session(cm, getOrCreateSecureRND());
	}

	/**
	 * Removes duplicates from a String array, keeps only first occurence
	 * of each element. Does not destroy order of elements; can handle nulls.
	 * Uses a very efficient O(N^2) algorithm =)
	 * 
	 * @param list a String array.
	 * @return a cleaned String array.
	 */
	private String[] removeDuplicates(String[] list)
	{
		if ((list == null) || (list.length < 2))
			return list;

		String[] list2 = new String[list.length];

		int count = 0;

		for (int i = 0; i < list.length; i++)
		{
			boolean duplicate = false;

			String element = list[i];

			for (int j = 0; j < count; j++)
			{
				if (((element == null) && (list2[j] == null)) || ((element != null) && (element.equals(list2[j]))))
				{
					duplicate = true;
					break;
				}
			}

			if (duplicate)
				continue;

			list2[count++] = list[i];
		}

		if (count == list2.length)
			return list2;

		String[] tmp = new String[count];
		System.arraycopy(list2, 0, tmp, 0, count);

		return tmp;
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @param ciphers
	 */
	public synchronized void setClient2ServerCiphers(String[] ciphers)
	{
		if ((ciphers == null) || (ciphers.length == 0))
			throw new IllegalArgumentException();
		ciphers = removeDuplicates(ciphers);
		BlockCipherFactory.checkCipherList(ciphers);
		cryptoWishList.c2s_enc_algos = ciphers;
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @param macs
	 */
	public synchronized void setClient2ServerMACs(String[] macs)
	{
		if ((macs == null) || (macs.length == 0))
			throw new IllegalArgumentException();
		macs = removeDuplicates(macs);
		MAC.checkMacList(macs);
		cryptoWishList.c2s_mac_algos = macs;
	}

	/**
	 * Sets the parameters for the diffie-hellman group exchange. Unless you
	 * know what you are doing, you will never need this. Default values are
	 * defined in the {@link DHGexParameters} class.
	 * 
	 * @param dgp {@link DHGexParameters}, non null.
	 * 
	 */
	public synchronized void setDHGexParameters(DHGexParameters dgp)
	{
		if (dgp == null)
			throw new IllegalArgumentException();

		dhgexpara = dgp;
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @param ciphers
	 */
	public synchronized void setServer2ClientCiphers(String[] ciphers)
	{
		if ((ciphers == null) || (ciphers.length == 0))
			throw new IllegalArgumentException();
		ciphers = removeDuplicates(ciphers);
		BlockCipherFactory.checkCipherList(ciphers);
		cryptoWishList.s2c_enc_algos = ciphers;
	}

	/**
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @param macs
	 */
	public synchronized void setServer2ClientMACs(String[] macs)
	{
		if ((macs == null) || (macs.length == 0))
			throw new IllegalArgumentException();

		macs = removeDuplicates(macs);
		MAC.checkMacList(macs);
		cryptoWishList.s2c_mac_algos = macs;
	}

	/**
	 * Define the set of allowed server host key algorithms to be used for
	 * the following key exchange operations.
	 * <p>
	 * Unless you know what you are doing, you will never need this.
	 * 
	 * @param algos An array of allowed server host key algorithms.
	 * 	SSH-2 defines <code>ssh-dss</code> and <code>ssh-rsa</code>.
	 * 	The entries of the array must be ordered after preference, i.e.,
	 *  the entry at index 0 is the most preferred one. You must specify
	 *  at least one entry.
	 */
	public synchronized void setServerHostKeyAlgorithms(String[] algos)
	{
		if ((algos == null) || (algos.length == 0))
			throw new IllegalArgumentException();

		algos = removeDuplicates(algos);
		KexManager.checkServerHostkeyAlgorithmsList(algos);
		cryptoWishList.serverHostKeyAlgorithms = algos;
	}

	/**
	 * Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm) on the underlying socket.
	 * <p>
	 * Can be called at any time. If the connection has not yet been established
	 * then the passed value will be stored and set after the socket has been set up.
	 * The default value that will be used is <code>false</code>.
	 * 
	 * @param enable the argument passed to the <code>Socket.setTCPNoDelay()</code> method.
	 * @throws IOException
	 */
	public synchronized void setTCPNoDelay(boolean enable) throws IOException
	{
		tcpNoDelay = enable;

		if (tm != null)
			tm.setTcpNoDelay(enable);
	}

	/**
	 * Used to tell the library that the connection shall be established through a proxy server.
	 * It only makes sense to call this method before calling the {@link #connect() connect()}
	 * method.
	 * <p>
	 * At the moment, only HTTP proxies are supported.
	 * <p>
	 * Note: This method can be called any number of times. The {@link #connect() connect()}
	 * method will use the value set in the last preceding invocation of this method.
	 * 
	 * @see HTTPProxyData
	 * 
	 * @param proxyData Connection information about the proxy. If <code>null</code>, then
	 *                  no proxy will be used (non surprisingly, this is also the default).
	 */
	public synchronized void setProxyData(ProxyData proxyData)
	{
		this.proxyData = proxyData;
	}

	/**
	 * Request a remote port forwarding.
	 * If successful, then forwarded connections will be redirected to the given target address.
	 * You can cancle a requested remote port forwarding by calling
	 * {@link #cancelRemotePortForwarding(int) cancelRemotePortForwarding()}.
	 * <p>
	 * A call of this method will block until the peer either agreed or disagreed to your request-
	 * <p>
	 * Note 1: this method typically fails if you
	 * <ul>
	 * <li>pass a port number for which the used remote user has not enough permissions (i.e., port
	 * &lt; 1024)</li>
	 * <li>or pass a port number that is already in use on the remote server</li>
	 * <li>or if remote port forwarding is disabled on the server.</li>
	 * </ul>
	 * <p>
	 * Note 2: (from the openssh man page): By default, the listening socket on the server will be
	 * bound to the loopback interface only. This may be overriden by specifying a bind address.
	 * Specifying a remote bind address will only succeed if the server's <b>GatewayPorts</b> option
	 * is enabled (see sshd_config(5)).
	 * 
	 * @param bindAddress address to bind to on the server:
	 *                    <ul>
	 *                    <li>"" means that connections are to be accepted on all protocol families
	 *                    supported by the SSH implementation</li>
	 *                    <li>"0.0.0.0" means to listen on all IPv4 addresses</li>
	 *                    <li>"::" means to listen on all IPv6 addresses</li>
	 *                    <li>"localhost" means to listen on all protocol families supported by the SSH
	 *                    implementation on loopback addresses only, [RFC3330] and RFC3513]</li>
	 *                    <li>"127.0.0.1" and "::1" indicate listening on the loopback interfaces for
	 *                    IPv4 and IPv6 respectively</li>
	 *                    </ul>
	 * @param bindPort port number to bind on the server (must be &gt; 0)
	 * @param targetAddress the target address (IP or hostname)
	 * @param targetPort the target port
	 * @throws IOException
	 */
	public synchronized void requestRemotePortForwarding(String bindAddress, int bindPort, String targetAddress,
			int targetPort) throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("You need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("The connection is not authenticated.");

		if ((bindAddress == null) || (targetAddress == null) || (bindPort <= 0) || (targetPort <= 0))
			throw new IllegalArgumentException();

		cm.requestGlobalForward(bindAddress, bindPort, targetAddress, targetPort);
	}

	/**
	 * Cancel an earlier requested remote port forwarding. 
	 * Currently active forwardings will not be affected (e.g., disrupted).
	 * Note that further connection forwarding requests may be received until
	 * this method has returned.
	 * 
	 * @param bindPort the allocated port number on the server
	 * @throws IOException if the remote side refuses the cancel request or another low
	 *         level error occurs (e.g., the underlying connection is closed)
	 */
	public synchronized void cancelRemotePortForwarding(int bindPort) throws IOException
	{
		if (tm == null)
			throw new IllegalStateException("You need to establish a connection first.");

		if (!authenticated)
			throw new IllegalStateException("The connection is not authenticated.");

		cm.requestCancelGlobalForward(bindPort);
	}
	
	/**
	 * Provide your own instance of SecureRandom. Can be used, e.g., if you
	 * want to seed the used SecureRandom generator manually.
	 * <p>
	 * The SecureRandom instance is used during key exchanges, public key authentication,
	 * x11 cookie generation and the like.
	 * 
	 * @param rnd a SecureRandom instance
	 */
	public synchronized void setSecureRandom(SecureRandom rnd)
	{
		if (rnd == null)
			throw new IllegalArgumentException();
		
		this.generator = rnd;
	}
}
